FIG. 5 is an exploded perspective drawing showing an example of the configuration of a frame, including a case, of a typical serial printer in the prior art.
As illustrated, a printer lower cover 1 is formed by plastic molding or aluminum diecasting, and its upper surface forms an open, shallow box. A ground plate 2 is positioned to cover the bottom surface of lower cover 1. In addition to acting as an electrical ground, ground plate 2 is used to increase the rigidity of lower cover 1. Mounted on a controller board 3 are circuit components or electrical parts for controlling the operation of the printer. The controller board 3 is superimposed over ground plate 2 and is attached thereto by several screws. A power unit (mainly composed of a transformer) 4 is also attached to ground plate 2 by means of screws or the like. Electrical cord 5 connects the power unit 4 to an external power supply.
A mechanical unit 6 includes those mechanically functioning components performing an actual printing operation. Unit 6 includes a mechanism frame 7, formed by plastic molding or sheet metal processing, to support the overall structure. A cylindrical platen 8 is installed with opposite ends thereof supported by opposite sides of the frame 7, so as to be rotatable. Also provided are a print head 9 having a tip placed in opposition to the platen 8, a carriage 10 on which the print head 9 is mounted and which is capable of spacing movement along the axial direction of platen 8, and a carriage shaft 11 which supports carriage 10, as well as various levers, rollers, guides, and the like. A plurality of connectors 12 connect respective components of mechanical unit 6. By connection to connectors of controller board 3 mounted on lower cover 1, connectors 12 establish an electrical connection to the components of the mechanical unit 6, i.e., the driver for the platen 8, the print head 9, and the carriage 10.
An upper cover 13 is formed, as is lower cover 1, into a box-shape opening downwardly, by plastic molding or aluminum diecasting. Cover 13 is attached so as to cover lower cover 1 and mechanical unit 6 which is attached to the lower cover 1. A platen knob 14 is attached to a platen shaft (not shown) which supports platen 8 of mechanical unit 6 through upper cover 13. By turning platen knob 14, platen 8 can be rotated. The upper cover 13 is provided at a rear, upper portion thereof with a medium ejection outlet 15. Print media on which printing has been conducted are ejected through ejection outlet 15. The upper cover 13 also has a sheet guide 16, which guides the print media after ejection thereof through ejection outlet 15.
To assemble the printer of the above configuration, first, controller board 3 and power unit 4 are attached and fastened, by fastening means such as screws, to the respective attachment locations of ground plate 2, which has been attached to the inner bottom surface of lower cover 1. Next, mechanical unit 6, including frame 7 in which are mounted platen 8 and carriage 10 on which print head 9 is mounted, is placed so as to overlie cover 1 and is also fastened thereto by screws. At this time the connectors 12 are plugged into corresponding connectors of board 3, and thus electrical connection of the components of mechanical unit 6 is obtained. Finally, upper cover 13 is connected from the top so as to cover both frame 7 and lower cover 1 and is fastened by screws at several locations. Assembly of the printer thus is complete.
FIG. 6 is an exploded perspective view showing another prior-art example, the mechanical unit 6 of which is slightly simplified. A difference from the previous example is that a paper chute 18, which guides to the platen the print medium on which printing is to be performed, and the lower cover are formed by integral molding. Note that in this figure the upper cover is omitted.
In FIG. 6, a lower cover 17 is formed by plastic molding or aluminum diecasting. The lower cover is formed by integral molding together with the paper chute 1 which guides a print medium on which printing is to be performed toward platen 8 of the mechanical unit. This eliminates the need to provide the mechanical unit with a paper chute, thereby making the structure simpler, smaller, and lighter. As with the example of FIG. 5, a controller board 3 for controlling and driving the printing operation and a power unit 4 are attached to lower cover 17 by fastening means such as screws. In addition, fastened to the bottom of lower cover 17, with screws as before, is a ground plate 2 to enhance the rigidity of lower cover 17 and to maintain an electrical ground potential.
A mechanical unit 19 has lateral side frames 19a and 19b which support plate 8, carriage shaft 11 which supports carriage 10 in such a way that carriage 10 is capable of spacing movement with print head 9 being mounted on carriage 10, support shaft 20 which also supports carriage 10, and the like.
To assemble the printer of the above configuration, first ground plate 2 is attached and fastened, by screws, to the bottom of lower cover 17. After that, controller board 3 and power unit 4 are fastened by screws, at respective locations behind paper chute 18, on lower cover 17. Next, mechanical unit 19 is attached by overlaying it from above in such a way that platen 8 of mechanical unit 19 conforms to paper chute 18 of lower cover 17. Unit 19 also is fastened at several locations by screws. Finally, an upper cover (not shown) is connected so as to cover lower cover 17 and mechanical unit 19. This completes the assembly of the printer.
However, the above described prior-art structures have the following problems.
First, in the example of FIG. 5, the configuration is such that controller board 3, power unit 4, and mechanical unit 6 are positioned over lower cover 1. Thereby, lower cover 1 and mechanical frame 7 form a double structure, and mechanical strength is increased. However, in addition to an increase in complexity due to an increased number of parts, assembly is time consuming since controller board 3 and power unit 4 must be attached to lower cover 1 and ground plate 2, respectively, by screws. Furthermore, electrical connections of controller board 3 and mechanical unit 6 must be made by connecting connectors 12 one by one.
In the other example shown in FIG. 6, mechanical unit 19 supports plate 8, carriage shaft 11, and support shaft 20 only by lateral side frames 19a and 19b. Therefore, rigidity of the assembly against bending and twisting is insufficient, and the print head gap is inconsistent. A large ground plate sometimes is used for reinforcement, but such arrangement is disadvantageous.